A Multichannel Noise Spectrum Analyzer for 10–10 000 Cycles

Abstract

A multichannel noise spectrum analyzer is described which allows the rapid measurement of flicker noise in vacuum tubes. The instrument gives either the equivalent saturated diode current or the equivalent noise resistance of the tube at 10, 30, 100, 300, 1000, 3000, and 10 000 cycles. The seven channels are read simultaneously; a whole spectrum may therefore be measured in 5 minutes. The instrument incorporates a quadratic thermistor-detector circuit with a dc voltmeter of variable time constant and wide-band filter circuits. The latter have a band width of 0.75 times the center frequency, but still give an accurate measurement of the noise at the center frequency. These large band widths reduce the time constant of the detector circuit needed for performing an accurate noise power measurement.